itertools: Add partial implementation.

itertools/itertools.py

@@ -0,0 +1,36 @@
+def count(start, step=1):
+    while True:
+        yield start
+        start += step
+
+def cycle(p):
+    while True:
+        yield from p
+
+def repeat(el, n=None):
+    if n is None:
+        while True:
+            yield el
+    else:
+        for i in range(n):
+            yield el
+
+def chain(*p):
+    for i in p:
+        yield from i
+
+def islice(p, start, stop=(), step=1):
+    if stop == ():
+        stop = start
+        start = 0
+    while True:
+        try:
+            yield p[start]
+        except IndexError:
+            return
+        start += step
+        if start >= stop:
+            return
+
+def tee(iterable, n=2):
+    return [iter(iterable)] * n